Analysis of Intelligent Traffic Collection Technology: Radar Induction Coil

    The technical framework of intelligent transportation mainly includes four parts: traffic collection, information transmission, information processing and information release. Traffic collection technology is an important common basic technology for the development of intelligent transportation. According to statistics from the Traffic Management Research Institute of the Ministry of Public Security, during the "Eleventh Five-Year Plan" period, the number of fixed traffic flow information collection points increased from 16,000 to 73,000, and the number of traffic monitoring points increased from 9,250 to 51,000. According to the market research results of Tranbbs, the overall market size of urban intelligent transportation will double in 2014 compared with 2010. Therefore, it is preliminarily predicted that the number of fixed traffic flow collection points will also double to about 150,000 points.

    From the perspective of technology type, the more common traffic data collection technologies in the current market include magnetic frequency vehicle detection technology, radio frequency vehicle detection technology, video vehicle detection technology, wave frequency vehicle detection technology, mobile traffic data collection technology, etc. Some technology types include several collection methods. In summary, the commonly used traffic data collection methods in the current market are mainly coils, videos, geomagnetism, ultrasound, radar, infrared, mobile phone terminals, floating vehicles, lasers, etc.

    Development History of Major Traffic Collection Technologies

    Induction coil

    In 1928, the world's first recognized vehicle detector appeared. It was a microphone installed near the road. The driver who passed by honked his horn to trigger the device to detect the passing of the vehicle. This detector was mainly used for signal control at intersections. At the same time, another device that began to be used was a pressure-sensitive vehicle detector. It was not until the 1960s that induction coils were used as vehicle detectors, becoming the most widely used detection system to date.

    video

    Video traffic detection was first proposed by California in 1976. Research on visual extraction of traffic parameters began in foreign countries as early as the 1970s. It entered the commercialization stage in the 1990s. China began to study video vehicle detection technology in the 1990s.

    my country's intelligent transportation market initially used imported products, with major manufacturers including Belgium's Traficon, the US ISS company's autoscope, and France's Citilog, which are still active in the domestic market. Domestic manufacturers include Chengdu Weilute and Dongshiyuan.

    Earth's magnetism

    The earliest use of geomagnetic vehicle detection products in my country was the Beijing Expressway Phase II entrance and exit signal control project around 2007. There were about 700 points installed, and the products were provided by Shanghai CCCC Intelligent System Engineering Co., Ltd. (the original technology belonged to Qinhuangdao Security Electronics Research Institute, and later acquired the technology products through capital operation). At that time, the product shape was cylindrical, with two in a group. This product is widely used in electronic police, checkpoints, traffic collection and signal control scenarios. Around 2009, several domestic geomagnetic manufacturers stood out from many participants, including Wuxi Perception Technology Co., Ltd., Mairui Data (Beijing) Co., Ltd., and Tianjin Shuntong Electronics Co., Ltd., which successively launched geomagnetic vehicle detector products.

    radar

    Since 1991, RTMS (Remote Traffic Microwave Detector) has been widely used in North America, Europe and Asia, and applied to intersection control systems, highway accident detection systems and traffic statistics. In the domestic market, China National Aero-Technology International Engineering Corporation developed and introduced RTMS in its overseas engineering contracting, and carried out Hanhua and supporting work for the full set of RTMS settings and analysis software. It was installed and used in the reconstruction of the second and third ring roads in Beijing from 2002 to 2003.

    Currently, the radar product manufacturers active in my country's intelligent transportation market include Wavetronix, RTMS, Olvia, and Smartsensor from the United States; domestic manufacturers include Dahua, Blue Shield Optoelectronics, Chuansu Microwave, Hefei Wenkang, and Shanghai Huichang.

    Introduction to Geomagnetic Sensor Technology

    Geomagnetic sensors are widely used in China mainly with the development of the Internet of Things, and have developed rapidly in recent years. Since early products were marketed too quickly when they were not mature, there are many doubts about the use of geomagnetic sensor products in the intelligent transportation industry.

    The technical principle of geomagnetic sensor is to use the iron material contained in the vehicle itself. When passing through the detection area, it will affect the change of the earth's magnetic curve in the area. The sensor can sensitively sense the change of magnetism and collect relevant data.

    A basic set of geomagnetic vehicle sensor products mainly includes three parts: vehicle detector, vehicle repeater and vehicle controller. At present, there are products on the market that have the transmission antenna built into the vehicle detector, but there are also some products that require a separate antenna or an external antenna.

    Vehicle detector: used to detect changes in the front-end magnetic field and detect data of vehicles in the lane;

    Vehicle repeater: When the distance is too far, a repeater is needed to enhance and forward the wireless signal;

    Vehicle controller: used to receive data from front-end detectors, manage multiple detectors, and transmit data to the data server.

    The technical threshold of geomagnetic sensor products is relatively low, which is one of the reasons why there are so many manufacturers in the market. However, when comparing the detection accuracy and service life of the products, the technical product gaps between manufacturers are still relatively large. The survey conclusions on the most questionable issues in the current market are as follows:

    Interference phenomenon

    There are two aspects of geomagnetic interference, one is the detection function, and the other is the communication function. Accuracy depends on many aspects including sensitivity, such as the quality of the sensor, the algorithm for processing raw data, and the reliability of communication. Interference in detection can be almost completely avoided by adjusting the sensitivity (magnetic resistance sensor). There are two types of interference in communication. One is pulse type, which interferes with you once in a while. This requires a reliable communication mechanism to solve. The other is suppression type interference, which requires adjusting the communication channel. At present, there are very few cases of suppressed communication interference in 2.4 frequency band applications.

    Battery life

    In the 2006 Beijing Expressway Entrance and Exit Signal Control Project, the short battery life of the geomagnetic vehicle sensor was one of the main reasons for the project's crux. At that time, the actual battery life did not exceed 2 years. The geomagnetic detector battery is mainly used to power the vehicle detection of the vehicle detector and the data transmission link of the repeater. The battery life of mainstream products in the current market can theoretically reach 10 years. In actual use, manufacturers use technologies such as "sleep" in the absence of vehicles. After actual testing in the traffic environment of first-tier cities, manufacturers can guarantee 5 years of use.

    In addition, some manufacturers' repeaters currently use 220V active power supply, but finding power supply on the road increases the difficulty of normal use of the system.

    Waterproof and dustproof

    Since geomagnetic detection products are installed under the ground, waterproof and dustproof is a key issue related to product quality. The dustproof and waterproof test can be achieved by the product shell, but the actual application environment is worse than the test environment. A large number of traffic and repeated squeezing by heavy vehicles may cause slight deformation of the shell in the long term, thereby reducing the waterproof and dustproof effect of the product.

    At present, there are products on the market that use silicone for sealing, which has better waterproof and dustproof effects. If such products need to be repaired, they can only be completely replaced, but the overall performance of the product is relatively good, the overall service life is relatively long, and the maintenance and replacement amount is within the acceptable range.

    Automatic fault alarm

    Since the batteries of geomagnetic products have a service life cycle and the waterproof and dustproof effects affect the normal use of the product, it is very important to monitor the battery power and automatically alarm for faults.

    Currently, there are not many manufacturers of geomagnetic vehicle detector products on the market that have data processing, analysis and system monitoring platforms, which is also a space for the future improvement of geomagnetic products.

    The choice of geomagnetic, radar and video technologies in traffic signal control scenarios

    In addition to the ring coil detection technology, which is currently widely used but is considered to have many disadvantages, geomagnetic, radar and video technologies are currently being proposed as alternative technologies for traffic flow collection in conjunction with intersection traffic signal control systems.

    Video technology traffic flow detection is linked with traffic signal control system, and the technical solution is relatively mature. A 5 million camera is responsible for one section, and three fill lights are equipped according to three lanes. The total cost is about 18,000 yuan (only refers to the product, excluding construction and installation costs, the same below). From a cost perspective, it is more applicable at intersections with more lanes. Although many video product manufacturers in the industry currently have this solution, the video also has the disadvantage of being significantly affected by the environment, and the actual market usage is still not large.

    Radar technology traffic flow detection is linked to traffic signal control systems and has been used in Hefei, Suzhou, Guangzhou and other places. A section of a radar product from a domestic brand costs about 10,000 yuan. A radar detection product at a point covers at least 3-5 lanes to ensure detection accuracy. Radar traffic collection has the disadvantages of vehicles blocking each other and inaccurate detection at low speeds, and the actual market usage is not large.

    The linkage between geomagnetic technology traffic flow detection and traffic signal control system has gradually attracted the attention of the industry in the past two years, and the overall investment in the project is lower than that of radar and video technology. The technical levels of various companies in the geomagnetic detector product industry are uneven, resulting in short service life and low accuracy, which are more troubling to users. According to Tranbbs's calculations, in 2013, geomagnetic vehicle detector products used for newly built traffic signal intersections accounted for approximately 10-15% of the total number of newly built traffic signal control intersections, and the usage has increased year by year.

    Any new technology needs to go through a dialectical development process before it can be maturely applied. The same is true for geomagnetic technology. From the perspective of the industry, we hope to see geomagnetic product suppliers provide convenient and reliable detection methods for the intelligent transportation industry with a responsible attitude, rigorous technology, and timely services.